If you print barcode as graphic, you can use any rotation level. In this case, NiceLabel creates an image of the barcode and sends it to the printer as graphic (bitmap).

If you print barcode as printer object, the rotation options are determined by the printer abilities. Usually, 90/180 degrees rotation is available. In this case, the printer received the commands to create the barcode on its own.

The control over object type (graphic/internal) is in Design ribbon tab>Printing Optimization (or in General tab in the property editor window).

So if go to barcode properties and check the box print barcode as a graphic I should be able to rotate it then? As I can't see the option to rotate, other than by 90 or 180 degrees as you mentioned previously.